1. Field of the Invention
The present invention relates to automated data storage libraries that manage the loading and unloading of portable data storage media to/from media drives as well as data exchange occurring with media loaded in such drives. More particularly, the invention concerns a data storage library featuring a dual purpose data/control path between a host computer and a media drive, this path conveying control signals and data between the host and drive, and also conveying robotic control signals from the host via the drive to a robotic device coupled to the drive.
2. Description of the Related Art
One of the most popular types of mass storage system today is the data storage “library”. Generally, a data storage library connotes a great number of commonly housed portable (“removable”) data storage media, which are transported among various storage bins and read/write media drives by a robotic device. These libraries have become popular for many reasons. First, the portable data storage media, usually magnetic tape or optical media, are typically quite inexpensive relative to other storage formats such as magnetic disk drives. Furthermore, libraries are easily expanded to accommodate more data, by simply adding more items of media. Additionally, most libraries can be easily updated with new equipment as it comes onto the market. For example, a new media drive may be introduced to the library to supplement or replace the existing media drives.
A number of different companies manufacture libraries today, each model displaying various different features and operating principles. One significant manufacturer of data storage libraries is International Business Machines Corp. (IBM), which provides a number of different libraries having widespread use and commercial success. Nonetheless, IBM has continually sought to improve various aspects of their libraries.
One area of focus is cost reduction, and more particularly, cutting hardware costs by designing libraries that share various components. It is often difficult, however, to design components that perform multiple functions or that respond to plural master units. Frequently, this level of flexibility requires the addition of a cumbersome layer of coordinating or supervising software code, which can ultimately reduce the performance of other unrelated aspects of the library. For instance, developing software to enable multiple incompatible hosts to manage a shared inventory of media items may be prohibitively difficult or expensive in many situations. Another difficulty concerns the need to prevent different hosts from interfering with each other's manipulation of media items in the shared library.
In other cases, a shared component may need to include another port for each host, thus increasing the hardware cost of the shared component. Furthermore, some configurations experience incompatibility when multiple components share a bus or other feature, resulting in reduced or lost data availability. Thus, engineers are confronted with a number of difficult challenges in their quest to consolidate components in a data storage library to reduce hardware expenses.